The long term goal is to improve function in children with cerebral palsy (CP). A selective dorsal rhizotomy (SDR) is performed to improve function by minimizing spasticity. A contraindication and limitation of the SDR is muscle weakness. Muscle weakness is related to reduced function. Thus, determining the degree of spasticity and strength/weakness in a child is a key consideration in the SDR selection process. Objective measures to assess spasticity and strength are not presently used in the process. In this study, objective measures to quantify spasticity and strength will be utilized to determine relationships between pre-surgery spasticity and strength and post-surgery functional measures. Based upon these relationships, an objective clinical tool to improve the selection of SDR candidates will be developed. In addition, comparisons of the measures among 4 different groups of children (n=40/group) will be made, those: 1) undergoing a SDR (SDR group), 2) undergoing physical therapy (PT) identical to the SDR group (PT group), 3) undergoing no change in current intervention (CP controls) and 4) having able bodies (AB controls). Specific Aim 1: Evaluate the importance of pre-surgery spasticity and strength as predictors of functional change due to SDR. Children from the SDR group will be tested on a dynamometer for spasticity and strength, evaluated using the Gross Motor Function Measure, have a gait analysis performed and answer a disability questionnaire. These assessments will be made 6 weeks and again 2 days prior to surgery, and at 8 and 20 months post surgery. Stepwise multiple regression with repeated measures will test the hypothesis that composite pre-surgery spasticity and strength from the ankles, knees, and hips in the SDR group will predict functional changes as a result of the SDR. Specific Aim 2: Compare impairment and functional measures among the SDR group, PT group and CP controls. The same assessments and testing sequence as the SDR group will be followed for these groups, but no surgery will be performed. ANOVA and ANCOVA will test the null hypotheses that the 3 CP groups will not change in impairment and function over all sessions and will not be different from one another. Specific Aim 3: Compare impairment and functional measures from 3 CP groups with those from AB controls. The children with able bodies will be assessed for spasticity, strength, and gait. ANOVA will test the null hypothesis that the CP groups will not be significantly different from the AB controls across all sessions. Descriptive statistics will describe the extent of differences from AP controls. The intent is that this investigation will improve the current methods for selecting SDR patients, thereby improving patient outcomes and reducing costs. It will also compare the efficacy of 3 modes of treatment for CP: SDR with intensive PT, intensive PT without SDR, and standard intervention.